Process for forming a diaphragm for use in an electrolytic cell

ABSTRACT

AN IMPROVEMENT IN THE OPERATION OF AN ELECTROLYTIC CELL HAVING A DIAPHRAGM POSITIONED BETWEEN AN ANODE AND A CATHODE OF THE CELL IS PROVIDED BY EMPLOYING A DIAPHRAGM COMPRISING AN ASBESTOS MATRIX IMPREGNATED WITH AT LEAST ONE OF A GROUP OF POLYMERS INCLUDING SYNTHETIC RUBBERS AND THERMOPLASTIC AND THERMOSETTING POLYMERS AND COPOLYMERS. A CONTROLLED AMOUNT OF THE POLYMERIC IMPREGNANT IS DEPOSITED IN THE SPACES BETWEEN THE ASBESTOS FIBERS TO PROVIDE CONTROLLED AND REPRODUCIBLE PERMEABILITY AND DENSITY IN A DIAPHRAGM HAVING GREATLY IMPROVED WET STRENGTH. BECAUSE OF THE SUPERIOR STRENGTH OF THE IMPREGNATED DIAPHRAGM, THEY CAN BE EMPLOYED IN THE ELECTROLYTIC CELL WITHOUT SUPPORT AND CAN BE SUBJECTED TO THE CONDITIONS OF LAMINATION SO AS TO BE COMBINED ON AN INSEPARABLE SHEET OR LAYER OF WIRE MESH OF A PLASTIC WOVEN FABRIC OR A SINTERED POROUS PLASTIC AND EMPLOYED IN LAMINATED FORM AS THE DIAPHRAGM IN AN ELECTROLYTIC CELL.

United States Patent 3,694,281 PROCESS FOR FORMING A DIAPHRAGM FOR USEIN AN ELECTROLYTIC CELL J oseph-Adrien Leduc, Short Hills, N.J.,assignor to Pullman Incorporated, Chicago, Ill.

No Drawing. Continuation-impart of application Ser. No. 814,821, Apr. 9,1969. This application Apr. 28, 1969, Ser. No. 819,998

Int. Cl. B01k 3/10; B3211 5/18; C03c 25/00 US. Cl. 156-77 2 ClaimsABSTRACT OF THE DISCLOSURE An improvement in the operation of anelectrolytic cell having a diaphragm positioned between an anode and acathode of the cell is provided by employing a diaphragm comprising anasbestos matrix impregnated with at least one of a group of polymersincluding synthetic rubbers and thermoplastic and thermosetting polymersand copolymers. A controlled amount of the polymeric impregnant isdeposited in the spaces between the asbestos fibers to providecontrolled and reproducible permeability and density in a diaphragmhaving greatly improved wet strength. Because of the superior strengthof the impregnated diaphragm, they can be employed in the electrolyticcell without support and can be subjected to the conditions oflamination so as to be combined on an inseparable sheet or layer of wiremesh of a plastic woven fabric or a sintered porous plastic and employedin laminated form as the diaphragm in an electrolytic cell.

This application is a continuation-in-part of copending application Ser.No. 814,821, filed Apr. 9, 1969, now abandoned.

This invention relates to an improved method for carrying outelectrochemical reactions in a system comprising an electrolytic celland more particularly relates to the use of a particular composition asthe diaphragm separating the anode chamber containing anolyte from thecathode chamber containing catholyte in the electrolytic cell.

In efie'cting electrochemical reactions, a separator is usually providedwithin the electrochemical cell to divide the cell into an anode chamberand a cathode chamber, the liquid medium contained therein commonlybeing referred to as the anolyte and catholyte, respectively. Theseparator may be formed such that the liquid medium is substantiallyprevented from passing between the chambers allowing only for thepassage of current or ionic transfer through the diaphragm separator.Such separators are referred to as liquid impermeable barriers ordiaphragms. These separators also may be such that the electrolyteactually flows therethrough from one chamber to the other, suchseparators thus being liquid permeable. Irrespective of whether theseparator is liquid impermeable or liquid permeable, it should beresistant to chemical deterioration caused by its contact with both theanolyte and the catholyte, the chemical properties of which are oftensignificantly different. For example, in the manufacture of molecularchlorine by the well known electrolysis of aqueous metal chloridesolutions, the anolyte is acidic and the catholyte is alkaline. Althoughcertain diaphragms composed entirely of white asbestos or chrysotile aresubstantially resistant to aqueous alkaline solutions, they undergorapid disintegration in an aqueous acidic medium. The deterioration ofwhite asbestos is aggravated in cells in which an initially formedelectrolyte soluble product is converted within the cell to anotherproduct which under operating conditions is produced in a gaseous state.Such a process is illustrated by the manufacture of propylene oxide bycontacting propylene 3,694,281 Patented Sept. 26, 1972 with anolyte inwhich halogen has been generated to form propylene halohydrin and thehalohydrin is dehydrohalogenated upon contact with the alkalinecatholyte to form gaseous propylene oxide.

Generally, the asbestos diaphragms used in commercial electrochemicalprocesses show some decline in mechanical strength when employed overextended periods of continuous operation. It has been proposed tostrengthen the asbestos matrix. While these binders have providedimproved results in increasing the mechanical strength of the diaphragm,the selection of binder has been limited to those types which have anatural affinity for the asbestos fiber or which can be made compatiblewith the fibers by the addition of surfactants so that they will adhereto the asbestos fibers when the binder particles are mixed as adispersion or emulsion with the asbestos in the form of a slurry. Mostof these additives, however, do not contribute to the strength orchemical resistance of the diaphragm and in some cases may even reduce,to some extent, the chemical resistance of certain asbestos materialssuch as chrysotile.

Certain electrochemical reactions provide for the separation ofintermediate products produced in the course of the reaction. In thesecases, it is desirable to employ a liquid impermeable diaphragm whichpermits only the passage of current therethrough. Although previousdiaphragms have been rendered substantially liquid impermeable, therequired thickness (about 300 mils) of such a separator causes it to beinconveniently employed in electrolytic cells of commercial design.

It is, therefore, an object of this invention to provide an improvementin the manufacture of chemicals in systems comprising an electrolyticcell in which the anode and cathode compartments are separated by adiaphragm, including power consuming as well as power producing cells.

Another object is to provide a particular diaphragm composition for usein such systems which has improved chemical and physical resistanceunder conditions of operation.

Another object is to provide a diaphragm having a composition selectedfrom a wide variety of components which enhance the properties of thediaphragm without the incorporation of non-beneficial secondaryadditives.

Another object is to provide a liquid impermeable diaphragm of greatlyreduced thickness.

Still another object of this invention is to provide a diaphragmcomposition which is suitably laminated on a porous plastic or metalsubstrate.

Another object of this invention is to provide an asbestos diaphragmcomposition of superior wet tensile strength.

A further object of this invention is to provide an asbestos diaphragmhaving a uniform composition and a controlled permeability.

A further object is to provide an improvement in the electrolyticmanufacture of halogen in a diaphragm-compartmented electrolytic cell.

A still further object is to provide an improvement in the manufactureof oxygenated derivatives of C to C olefinic compounds in anelectrochemical system comprising a diaphragm-compartmented electrolyticcell.

Various other objects and advantages of this invention will becomeapparent to those skilled in the art from the accompanying descriptionand disclosure.

According to this invention, an improvement is provided in anelectrolytic cell in which it is desired to separate portions of theelectrolyte while allowing at least the flow of electrical currentbetween the opposing electrodes, which improvement comprises operatingthe cell with an impregnated asbestos diaphragm positioned where suchseparation is desired.

The asbestos comprising the matrix of the present diaphragm can be ofthe serpentine type such as, for example, chrysotile, which is amagnesia silicate having a magnesia content of from about 39 to about 44percent, or the matrix can be composed of asbestos of the amphiboletype, such as crocidolite, amosite, anthophyllite, tremolite andactinolite or blends of these types of asbestos materials. Such matricescan be prepared on a Hand-sheet paper-making machine and provide a papermatrix of substantially pure asbestos fibers. The asbestos matrix canalso be composed of any of the above asbestos types or blends of thesetypes wherein other additives, such as binders or binder compositions,are incorporated. Suitable binders and binder compositions are thosewhich are disclosed in copending Application Ser. No. 814,821, filedApril 9, 1969, and which are herein incorporated by reference. Of thesebinders, high polymers and copolymers of butadiene, vinyl chloride,ethylene, propylene and tetrafluoroethylene are preferred. The matricescomposed of asbestos and binder are referred to as asbestos matrixcompositions and are generally prepared by mixing and paper manufacturein a Fourdrinier paper-making machine. The preferred asbestos matricesare those of the amphibole type having a magnesia content of from toabout 20 weight percent, most preferably a magnesia content of from 0 toabout 8 percent by weight of magnesia such as the types known ascrocidolite and amosite. Because of the high magnesia content aboveabout 20 percent of certain other asbestos, it is desirable that theyare employed as a blend with low magnesia amphibole types.

The accepted formula for crocidolite, which is a sodium iron silicate,is Na O-3FeO-Fe O -8SiO -H O, although some grades may additionallycontain small amounts of magnesia, for example, up to about 3 weightpercent. Actinolite is a calcium magnesia iron silicate having anempirical formula Ca (MgFe) Si O (OH) which has a magnesia content, forexample, up to about 18 percent. Amosite is a low-magnesia iron silicate(for example, from about 1 to above 7 weight percent magnesia) theformula for which is expressed as Fe Mg Si O (OH) Crocidolite asbestosis commonly referred to as blue asbestos, although it is to beunderstood that often other amphiboles having magnesia content less than8 percent are also referred to as blue absestos. Any of the aboveasbestos types, blends of asbestos types, which may or may not containbinders and other additives such as plasticizers, surfactants, etc., aresuitably employed as the dried paper or matrix composition which issubjected to the impregnation of the present invention. It is to beunderstood, however, that the matrix composition employed in the presentprocess may be dried only to the extent that they provide a formed sheetand not subjected to temperatures which would render them anhydrous.Thus, the matrices employed in the impregnation operation actually canbe in a wet or dry form.

Suitable impregnants employed as solutions for incorporation into thematrices of the present invention are any of those materials disclosedas binders in my copending application Ser. No. 814, 821, filed April 9,1969, as well as other polymeric compounds, such as cotton, nylon, orlonfibers, which do not posses afiinity for the asbestos fibers and whichare substantially insoluble in aqueous media. Since the purpose of theimpregnant is to fill the pores or spaces between the asbestos fiber ofthe matrix, it need not adhere or be compatible with the abestos fibers.Thus, the selection of desired compositions for the diaphragn can beextended to compounds which have not previously been employed withabsestos but which provide beneficial properties in the diaphragmcompositions of the present invention.

The impregnation of the matrix also provides for more uniformdistribution of polymeric particles in the matrix and allows forcontrolling the permeability of the diaphragm to low levels, if desired,by directly controlling the concentration of the impregnant in theliquid medium applied to the asbestos matrix. Thus, a diaphragm of muchhigher density per diaphragm thickness can be produced than anypreviously obtainable. For example, a liquid impermeable diaphragm canbe produced WhlCh has a thickness not greater than mils. In general, thediaphragms of the present invention can be made to provide a controlledand reproducible permeability best suited for the requirements of aparticular electrochemical reaction.

Another improvement in the diaphragms of the present invention isevidenced by the greatly improved wet tensile strength of the diaphragmstructure which allows operation of the electrochemical process in acontinuous manner for periods of more than one year withoutinterruption.

Specifically, the impregnants of the present invention comprise highpolymers of the rubber type, such as polychloroprene (neoprene),polyisobutylene, polybutadiene, polydimethylbutadiene,polymethylbutadiene (isoprene), polyvinyl chloride and butadienepolymers and copolymers with styrene and acrylonitrile and organicpolysulfide types such as the ethylene chloride-sodium tetrasulfide anddichloroethyl ether-sodium tetrasulfide copolymers, and thermoplasticand thermosetting polymers and copolymers, such as polyethylene,polypropylene, polybutylene, polystyrene, polystyrol,polytetrafluoroethylene, polychlorotrifluoroethylene, polyvinylidenechloride, polyacrylonitrile, polyester, chlorinated polyvinyl chloride,polyurethane, polyvinylpropionate, polyvinylacetate and acrylic,cellulose acetate and methacrylate polymers and copolymers such asbutadiene-styrol, and any of the known copolymers which combine monomersof the above mentioned polymers.

The compositions used as impregnants can be employed in mixture and maycontain resinous thickening agents such as methyl cellulose known asMethocel and a hydrophilic colloid such as Carbopol which providethixotropic properties and increased resistance to separation ofimpregnant from the matrix.

Preferred impregnants of the above group of polymeric materials are thepolymers and copolymers of butadiene, vinyl chloride, chloroprene,isoprene, polyethylene, polybutylene, polypropylene,polychlorotrifluoroethylene, and polytetrafluoroethylene.

Polytetrafiuoroethylene, known as Teflon, is commercially supplied in ahydrophobic colloidal dispersion of negatively charged particles (0.05to 0.5 micron) suspended in water. These colloidal dispersions areideally adapted for incorporating impregnant into an asbestos sheet inthe manufacture of the diaphragm. The aqueous dispersions are providedin various concentrations containing from about 30 percent to about 65percent Teflon solids.

Polyethylene aqueous dispersions are also supplied commercially underthe trade name Microthene dispersions. The size of the polymer particlesin the dispersion range from 8 to 30 microns and dispersions of from 10percent to 70 percent solids are available. Aqueous organic dispersionsof up to 55 percent solids are marked for polyethylene.

Because impregnation is employed in incorporating polymeric materialsinto a preformed asbestos matrix, the additive is not limited to aqueousmixtures which in other techniques of incorporation must be mixed withan aqueous slurry of asbestos fibers. In the present invention where theasbestos sheet is already formed, the impregnants are incorporated bythe use of solutions, emulsions or dispersions of impregnant either inorganic liquids or in water, depending upon the impregnant selected.

Non-aqueous or aqueous solutions of the following liquids can beemployed as carriers for the impregnant which is contained in the liquidin a concentration of between about 50 and about 98 weight percent.Suitable liquids include hydronaphthalenes, such as Decalin andTetralin, toluene, ethyl acetate, mineral spirits, ethanol,methylisobutyl ketone, tetrachloroethylene, trichloroethylene, amylacetate, xylene, dichloroethane, methyl ethyl ketone, methylenechloride, dichloropropane, ethyleneand propylene-chlorohydrins, etherand esters. Observance of the solubility of impregnants in certainorganic liquids should be keyed to the type of electrochemical processin which the diaphragm is to be employed. Thus, an impregnant which issoluble in chlorohydrin, dichloropropane, dichloroethane, dichloroether,or alcohols, should obviously not be employed in organic processes suchas the propylene oxide process where chlorohydrin or a product similarto the solvent is produced as an intermediate or final product of thereaction. However, impregnants which are soluble in these solvents aresuitably employed in the electrolytic process for the preparation ofhalogen which employ cells containing a solid anode and cathode as wellas cells containing a mercury amalgam cathode. Of the above list ofsuitable solvents or dispersants, water, Tetralin, Decalin,dichloroethane and methyl isobutyl ketone are preferred.

The general impregnation procedure comprises impregnating an asbestosmatrix with a degradation resistant material to strengthen the asbestosmatrix in the resulting diaphragm material. Impregnation with theabovementioned impregnants affords control of diaphragm characteristicssuch as permeability, strength, thickness and voltage drop through theresulting diaphragm.

The procedure of incorporation applies to an asbestos matrix which maybe in the form of a sheet or mat made from pure or admixed fibers whichmay or may not contain a binder, a surfactant, a precipitating agent orother solid additive. Between about 0.1 and about 50 weight percentpreferably between about 2 and about 20 weight percent of impregnant isincorporated into the asbestos matrix. The procedure comprises treatinga formed asbestos matrix in a dry or damp state by spraying with animpregnant containing solution or by immersion in a tank containing adispersion, emulsion or solution of the impregnant. In the latterprocedure, the preformed asbestos matrix is passed through the tank ofliquid containing impregnant while permitting a residence time in thetank of from about 0.1 to about 60 minutes for impregnation to beeflfected. The immersion liquid is maintained at a temperature of fromabout 20 C. to about 250 C. and agitation of either the matrix and/orthe immersion liquid may be provided, if desired. After immersion for asuitable period, the impregnated matrix is withdrawn from the tank andallowed to drain so as to remove a major portion of the mother liquor.Pressing the impregnated matrix to assist in the removal of motherliquor can be accomplished by passing the impregnated sheet between apair of pressure (1 to 50 p.s.i.g.) rollers or pressing plates which arepreferably adapted to return the liquid to the immersion tank.Alternatively, the impregnated sheet can be treated for removal ofliquid by suction or can be pitched at an angle to remove liquid. Theentire procedure of immersion and drainage can be repeated or theasbestos mat can be subjected to a succession of immersions in the tankprior to pressure drainage when it is desired to incorporate additionalamounts of impregnant in the asbestos matrix.

The drained impregnated matrix or sprayed matrix is subsequentlysubjected to drying, preferably by the use of heated rollers, heatedplates, or a heated chamber maintained at a temperature between about 25C. and about 120 C. depending upon the flash point of the solventemployed. After drying in the drying zone, the impregnated diaphragm maybe heat treated at a higher temperature to the sintering temperature ofthe impregnant, for example, from about 40 C. to about 400 C. so as tocause adhesion of impregnant particles in the pores and/or on thesurface of the asbestos matrix of the diaphragm. The heat settingoperation can be controlled to sinter either impregnant particlesdispersed throughout the matrices or to affect sintering of particles ononly one or both surfaces of the matrix.

It is to be understood that additional steps or stages can be interposedor added to the sequence of steps recited above. For example, calenderrollers can replace the drain rollers in the above procedure and apressure from 50 to 1500 p.s.i.g. preferably between about 50 to 1000p.s.i.g., can be applied to the wet impregnated asbestos sheet. Usually,the higher pressures are applied when a high density diaphragm isdesired and when it is desirable to reimmerse the impregnated sheet inthe same or a different impregnating liquid.

A laminaton of the impregnated diaphragm can be combined with the aboveimpregnation technique. For example, the dried asbestos paper sheet ormat can be passed into a hot solution of impregnant such as, forexample, polyethylene in a hot Decalin solution and impregnated to adesired level before removing and draining the impregnated mat. Theimpregnated mat can then be pressed to a desired uniform thickness, forexample, from 10 to 50 mils, and partially dried before passing the matto a second immersion tank or it can be directly introduced therein. Thesecond immersion tank contains a solvent for the impregnant distributedin matrix during the first immersion and this solvent is maintained at atemperature sufficient to cause softening of the impregnant particleseither on the surface of the mat or throughout the mat structure. Thesolvent treated mat is subsequently passed through a second pair ofcalender rollers adapted to drain solvent back into the second immersiontank and finally transferred to a drying and compression zone wherein itis applied to a substrate, for example, a porous plastic material orwire screen, and pressured under a pressure of from about 10 p.s.i.g. toabout 1000 p.s.i.g., at a temperature from about 40 C. to about 250 C.The substrate which is a foraminous material, may be composed of glass,metal or a woven or knitted material.

A convenient method of applying the impregnated asbestos to thesubstrate comprises simultaneously feeding a sheet of impregnateddiaphragm material and the substrate over at least one pair of calenderrollers, thereby heating under sintering conditions while compressing toform a strong adhesive layer. It is to be understood in the aboveembodiment that the second immersion tank containing only solvent can beomitted when the temperature of the first immersion tank and theconcentration of impregnant solution in the first immersion tank iscontrolled to maintain softening of at least the impregnant particlesdistributed on the surface of the asbestos matrix.

Another embodiment for forming a laminate comprises coating'the surfaceof the substrate with particles of the impregnant at sinteringtemperature or applying sutficient- 1y hot solvent for the impregnant tothe surface of the substrate so as to soften the surface and pressingthe impregnated asbestos mat to the surface of the substrate undersintering conditions. In this way threads, fibers or particles may beimbedded in the interface between the impregnated asbestos and thesubstrate. The amount of plastic incorporated into the asbestos matrixmay vary from complete impregnation or saturation to the minimumrequired to bond the reinforcing material. Generally, high impregnationresults in increased density of the diaphragm.

Other methods of lamination will become apparent to those skilled in theart from the accompanying description and disclosure. For example, itwill be apparent that the substrate can be applied to one or bothsurfaces of the impregnated asbestos matrix or the impregnated asbestosdiaphragm can be applied to one or both surfaces of the substrate.

Also, other methods of forming the diaphragm may be employed, such asplacing the asbestos mat directly on a stainless steel wire mesh cathodeand spraying or dipping the cathode assembly so that the asbestos matrixbecomes impregnated and finally drying the impregnated diaphragmdisposed on the cathode which is then employed in the operation of theelectrolytic cell.

The density of the diaphragm of the present invention varies over a widerange depending upon the degree of permeability desired. Thus, thedensity can be varied from about 0.3 gram to about 1 gram per cc.,preferably from about 0.4 to about 0.7 gram per cc. If the diaphragm isto be liquid permeable, it is preferred that the density or thickness ofthe diaphragm be such as to permit an electrolyteflow rate through thediaphragm of from about to about 2000 cc. per minute per square foot ofdiaphragm. When chlorine is the intended end product of theelectrochemical cell, the flow rate of electrolyte through the diaphragmis from about 20 to about 300 cc. per minute per square foot ofdiaphragm, preferably from about 10 to about 50 cc. per minute persquare foot of diaphragm. However, when an olefin oxide is the intendedend product, the flow rate is from about 100 to about 2000 cc. perminute per square foot of diaphragm, preferably from about 200 to about1000 cc. per minute per square foot of diaphragm. Substantially liquidimpermeable diaphragms have a permeability as low as 0.05 cc. per minuteper square foot of diaphragm.

The impregnated asbestos matrices of the present invention displaygreatly improved mechanical strength when employed under conditions ofcontinuous operation in an electrolyte cell containing an aqueouselectrolyte solution. The mechanical strength of the diaphragms of thepreesnt invention are measured by the wet tensile strength (dead weight)method. Generally at least 50% improvement over non-impregnateddiaphragms is realized.

The wet tensile strength of the diaphragm measured in the examples isexpressed as the number of grams weight necessary to cause rupture ofthe diaphragm material at the isthmus. Each sample tested has a width of6 cm. at its widest point and a length of 14 cm. Midway between theends, the sample has a narrow isthmus 1 cm. wide which extends /a of thelength of the sample. The samples are cut to a uniform size by means ofa stencil and are soaked in water at room temperature for 3 hours beforetesting. The test comprises clamping the sample at one end to a supportand clamping the other end to a scale to which weights are added untilthe sample ruptures at the isthumus.

The preferred electrolyte which is charged to the electrolytic cell isan aqueous solution of a metal halide, chlorides and bromides being mostpreferred. Usually employed are the halides of sodium, potassium,lithium, barium, calcium, strontium, magnesium or mixtures thereof.

A mixed electrolyte system can be employed for improving theconductivity inasmuch as the metal hydroxide which forms at the cathodeis utilized within the system and since economics of the process doesnot depend upon recovery of hydroxide as a product of the process, mixedelectrolytes are useful and, from the standpoint of improvement ofconductivity, are advantageously employed. Salts which can be added toincrease the electrical conductivity of the electrolyte include solublealkali metal, and alkaline earth metal sulfates, sulfides, chromates,phosphates and carbonates, such as sodium sulfate, potassium sulfate,lithium sulfate, calcium sulfate, sodium sulfide, potassium sulfide,lithium sulfide, sodium nitrate, calcium nitrate, potassium nitrate,lithium nitrate, sodium chromate, potassium chromate, potassiumdichromate, calcium chromate, sodium orthophosphate, sodiumpyrophosphate, potassium carbonate, sodium carbonate, lithium carbonate,etc. The promoters of conductivity can be used in amounts from about 1to about 25 weight percent or more of the electrolyte solution. In thepreferred aqueous electrolyte solutions, the metal halide content canvary from dilute to saturated solutions which are usually charged to andwithdrawn from the cell at a rate of from about 10 to about 1000 cubiccentimeters per minute per square foot of apparent electrode surfacewhere the area of electrode is equal to the area of the diaphragm. Mostpreferably the electrolyte is present in aqueous solution in aconcentration of between about 2 and about 35 Weight percent. In somecases the electrolyte solution contains solid particles which adhere tothe diaphragm as it is passed therethrough. When such solid particlesbecome troublesome, the flow of electrolyte in the cell and through thediaphragm can be reversed in order to dislodge the solid impuritieswhich may be deposited on one side thereof.

The diaphragm of the present invention may be disposed in a horizontalor vertical position within the cell between the anode and the cathodethereby dividing the cell into an anode chamber and a cathode chamber.The diaphragm can be mounted against the cathode or against a barrierdisposed in the cell in spaced relationship between the anode and thecathode or it can be unsupported, or substantially unsupported exceptfor a frame which is positioned in the cell by retaining means. In thelatter case mechanical support can be supplied by transyersing the frameholding the diaphragm with one or a plurality of threads, e.g., plasticfilaments on one or both sides of the diaphragm surface. This type ofmechanical support is beneficial in reinforcing diaphragms which areretained in frames or clamping means within the cell but which are notsupported on one of their surfaces by a barrier or cathode screen.

The permeability of the diaphragms of the present invention can varyover a wide range so that between about 0.1 and about 2000 cc. of liquidcan be passed per minute per square foot of diaphragm surface. Thethickness of the diaphragm generally varies from about 10 to about mils,preferably from about 20 to about 50 mils. In certain processes in whichit is desirable to separate and recover an intermediate product of areaction, a liquid impermeable diaphragm may be desired, such as thediaphragm of 250 mils thickness.

In a preferred aspect of this invention, a method is provided whichcomprises subjecting an aqueous medium contained in adiaphragm-compartmented electrolytic cell and having a halideelectrolyte dissolved therein to the action of a direct electric currentto generate halogen at the anode and hydroxyl ion at the cathode in thecathode compartment, introducing an olefinic compound into the anolyteand reacting this olefim'c compound with halogen produced in the aqueousanolyte thereby forming the halohydrin derivative of the olefin, passinghalohydrin containing electrolyte through the diaphragm,dehydrohalogenating the halohydrin to olefin oxide in an alkalinecatholyte produced at the cathode of the cell, separating olefin oxidefi'om the aqueous medium, and recycling aqueous electrolyte to the anodecompartment of the electrolytic cell.

The halohydrin forming reaction may be effected by contacting the olefinwith anolyte 'within the cell or in a contacting tower external of thecell proper or partially in both. The halohydrin containing aqueousmedium is then subjected to dehydrohalogenation in order to convert thehalohydrin to olefin oxide by treatment with the catholyte which isalkaline due to the cathodic reaction which results in the formation ofhydroxyl ion. The dehydrohalogenation may be effected in the alkalinecatholyte contained within the cell or in a step external of the cell orpartially in both. These various methods are described in further detailin US. Pat. No. 3,288,692 and Belgian Pats. No. 705,083 and No. 705,084,the details of which are incorporated by reference herein.

The present process can be applied to any electrochemical processwherein an unsaturated organic compound is oxidized. Illustrative ofprocesses in this category other than the preferred process describedabove, are

the electrochemical processes for producing a glycol from an olefin oran olefin from acetylene in addition to olefin oxide from olefin asdescribed and referred to in U.S. Pat. No. 1,253,617.

The anode of the cell comprises a solid or a porous material or asubstrate having distributed thereon electrolyte-porous andelectrolyte-impervious surfaces and can also contain a hollow core or aninternal chamber for the introduction of the organic reactant into theelectrolyte solution. The anode may be composed of graphite, platinum,platinized titanium, platinized tantalum, titanium coated with a mixtureof platinum and at least one other noble metal such as iridium orrhodium, platinized iridium, magnetite, titanium, lead, or an inertsubstrate such as polyethylene, polypropylene, polyurethane, Teflon, ora perfiuorochloro plastic, etc. metallized with copper or silver andhaving platinum deposited thereon as the metal which is exposed to theelectrolyte medium. Electrodes of the latter type are prepared inaccordance with the techniques described in US. Pat. No. 3,235,473. Thepreferred anodes of the present invention, however, comprise a metalsubstrate, most preferably titanium, coated with a noble metal or alloyof a noble metal in the form of elemental metal or metal oxide asdescribed and referred to in US. Pat. No. 3,379,627.

The cathode may be composed of any conductive material which ischemically inert to caustic and is usually composed of steel, stainlesssteel or an amalgam such as the amalgam cells described or referred toin US. Pats. No. 3,394,059 and No. 3,288,692. The cathode is more oftenin the form of a ferrous metal screen or expanded sheet and may be usedin contact with or separated from the diaphragm.

The organic reactant of the present invention is an olefinic compound,that is, a compound having at least one ethylenically unsaturatedcarbon-to-carbon double bond which is the reactive site at which theoxygen linkage is formed during the process. Included within the scopeof the invention is the use of the unsubstituted and aryl and/or halogensubstituted acyclic and alicyclic monoolefins and polyolefins includingstraight and branched chain olefins, as well as those in which theethylenic double bond is in the terminal or non-terminal position orwithin a cycloaliphatic ring. The olefin may be normally gaseous orliquid. Olefins may be diluted with any suitable inert solvent such as aparafiinic or aromatic hydrocarbon or mixtures thereof includingpetroleum fractions such as kerosene, etc. Other liquid diluents includecycloheXane, toluene, benzene, xylene, hexane, heptane, iso-octane andthose mentioned in US. Pat. No. 3,394,059.

Typical examples of suitable olefins for use in the preferred process ofthis invention are the alkenes of the homologous series C H wherein n isan integer from 2 to 12, such as ethylene, propylene, butene, pentene,hexene, heptene, dodecene, etc., including olefins in which the doublebond is in a non-terminal position, such as 2-butene, 2-pentene, etc.,and branched olefins such as isobutene, isopentene, 4-ethyl-2-hexene, aswell as branched compounds in which the double bond is in the sidechain, such as Z-methylene pentane and alkenyl compounds, such as4-propene-4-yl-octane and cyclic olefins, such as cyclopentene,cyclohexene, cyclooctene, cyclononene, etc. Polyolefins may also bereacted in the electrochemical reaction of the present invention.Suitable polyolefins include those containing isolated, cumulative orconjugated double bonds, such as diallyl, allene, butadiene, isoprene,2,3-dimethylbutadiene, etc. As pointed out above, olefins substitutedwith aryl and halogen groups, such as, for example, styrene, stilbene,allyl chloride, chloropropene, vinyl chloride, vinyl bromide, etc. mayalso be used as the olefin reactant in the present process.

The olefin need not be pure and may contain paraflinic or otherimpurities or diluents normally found in commercially available olefins.For example, commercial grades of ethylene and propylene are suitableand normally contain low molecular weight paraffins, such as ethane,propane, etc. When a low molecular weight olefin is reacted, a gaseousdiluent, such as nitrogen, methane, ethane, propane, etc. may be admixedwith the olefin and may be used in amounts between 5 and about 95 volumepercent of the total feed.

The throughput of olefin through the anode compartment or a reactionspace outside of the electrochemical system may be selected in such way,for example, that approximately 5 to 95 percent is converted per singlepass. It has been shown to be an especially favorable technique tointroduce into the anode compartment or conversion chamber a gaseousmixture of the olefin to be converted and an inert gas, theconcentration of olefin in the mixture amounting, for example, to 25 to65 volume percent, preferably 35 to 55 volume percent and to convert persingle pass of the gaseous mixture through the anode compartment orconversion chamber, 75 to 95 percent, preferably 30 to percent of theintroduced olefin. As inert gas, the gaseous paratfins corresponding tothe olefin used are especially suitable.

In the diaphragm-compartmented electrolytic cell wherein olefin isreacted to form halohydrin and the halohydrin is dehydrohalogenated toform olefin, a gaseous efiiuent is withdrawn from the anode section ofthe cell which contains unreacted olefin and dihaloparaffinic derivativeas a by-product of the process and a gaseous efiiuent containing aportion of the olefin oxide product and hydrogen is recovered from thecathode section of the cell. After the olefin oxide is formed in thecatholyte, the resulting electrolyte solution is passed into aseparation or stripping zone wherein dissolved oxide product isseparated from the electrolyte by distillation and/ or by means of astripping gas, such as nitrogen, steam, methane, ethane, etc. or anyother gas which is inert to the oxidation product. The olefin oxide canthen be subjected to further purification, if required, and recovered asa product of the process.

The resulting electrolyte solution separated from the oxide product,usually contain contaminants which form a tarry or tacky coating on theanode of the electrolytic cell. Therefore the separated electrolyte isgenerally subjected to decontamination, e.g., by treatment with anoxidant treatment followed by filtration prior to recycle as describedin copending applications Ser. No. 809,961 Ser. No. 809,962 both filedon Mar. 24, 1969. The pH of the recycle electrolyte is adjusted withacid, e.g., a hydrogen halide to maintain a desired pH range in theelectrolytic cell, usually, between about pH 6 and about pH of 12.

The electrolytic reaction zone may be operated over a wide range ofcurrent density such as between 20 and about 1500 amperes per squarefoot of apparent electrode surface. The operating voltage of the cell isat least the voltage required to obtain electrolysis of the metalhalide. The minimum voltage, therefore, depends upon the particularelectrolytic system. For example, when sodium chloride is used as thesource of halogen for the halohydrin intermediate, a voltage of at least2.2 volts is required, assuming unit activities and standard conditions.Usually the voltage applied is within the range of between about 3 andabout 7 volts. In operation, however, the voltage demand is increasedabove the minimum or decomposition voltage due to a combination of avariety of factors such as, for example activity and overvoltage. It hasbeen found that the olefin reactant introduced to the vicinity of theanode reduces the electrode overvoltage depending upon the particularanode material. In this connection, porous, hollow anodes instead ofsolid electrodes can be used to introduce the olefin to the anode in aWay such that the olefin reactant diffuses through the pores werecontact between the olefin, electrolyte and electrode occurs therebyproducing product, reducing overvoltage and polarization. Theoretically,during operation, the current density can be varied within a desiredrange or the current may be reversed to minimize polarization.

The electrolytic cell can be operated over a relatively wide range oftemperatures and pressures, i.e. from about C. to the boiling point ofthe aqueous electrolyte which, at atmospheric pressure, is usually about105 C. A pressure within the range of subatmospheric, for example about0 p.s.i.g., to 300 p.s.i.g. or more can be employed. The temperature andpressure are interrelated to the extent that they are controlled tomaintain the aqueous electrolyte system in the liquid phase. Thus, whenthe cell is operated at a temperature above the atmospheric boilingpoint of the aqueous electrolyte system, the cell is operated at apressure sufliciently high to maintain the liquid phase.

Having discussed many aspects, reference is now hadto the accompanyingexamples which further illustrate the invention. It is to be understood,however, that these examples are presented for a better understandingand are not to be construed as unnecessarily limiting to the scope ofthis invention as set forth and described in the foregoing disclosureand the claims.

EXAMPLE 1 A blue asbestos sheet composed of crocidolite fibers is madefrom an aqueous slurry containing 80 grams of the fibers in a Hand-sheetmachine. The sheet is compressed under 100 p.s.i.g. between twostainless steel plates to a thickness of 68 mils and dried. The driedasbestos sheet has a wet tensile strength of 150 grams. A solution of 75grams per liter of polyethylene dissolved in decahydronaphthalene ismade by stirring low density (density of 0.90 to 0.92) polyethylene intoa Deoalin solution (decahydronaphthalene) heated to a temperature ofbetween 100 C. and 113 C. The solution is then introduced into animmersion tank and is heated therein to a temperature of 115 C.

The blue asbestos sheet of 68 mils thickness is placed between two x 10mesh stainless steel screens. This assembly of the asbestos sheetbetween screens is preheated by holding it over the hot liquid in theimmersion bath for 1 minute. After preheating, the assembly is immersedin the impregnation solution in the immersion tank and agitated every 20seconds for a period of about 2 minutes. The resulting impregnatedasbestos paper is then withdrawn from the impregnating solution andtilted on the stainless steel screen (at an angle of about 45) for aboutseconds to allow for drainage of mother liquor into the immersion tank.The drained impregnated asbestos is then air dried for 2 minutes betweenthe screens after which the upper screen is removed and the impregnatedasbestos sheet is turned over onto a polished stainless steel platelocated in a separate drying zone whereon it is vacuum dried at 75 C.for 24 hours.

The impregnated diaphragm is removed from the drying zone and measuredfor wet tensile strength. The impregnated blue asbestos shows a wettensile strength of 4196 grams.

EXAMPLES 2 THROUGH 11 An aqueous solution of Teflon is made from anemulof a negatively charged hydrophobic colloid containing Teflon resinparticles of from 0.05 to 0.5 micron. The Teflon emulsion contains 59%by Weight solids and is stabilized with 6% of a nonionic wetting agentsuch as an alkyl aryl polyether alcohol, sulfonate or sulfate (in thiscase, Triton X-100). The solution is diluted with water to aconcentration of from 6 to 12 weight percent Teflon and introduced intoan immersion tank.

A blue asbestos paper having a thickness of 0.040 inch containing 4%copolymer of butadiene and styrene (buna- S) as a binder is placedbetween 2 screens and is immersed in the impregnating solution for 1minute. After thorough wetting of the paper with the solution, the paperand the screen assembly are removed from the tank, pitched at TABLE IImpregnant solution Wt. Permea- (wt. percent bi lity 1 percent increaseof Example Teflon) of sample sample 1 Expressed as head of waterpressure in inches at a fixed flow rate of 300 ccJminute/square foot ofdiaphragm.

I Double immersion of sample at 1 mmute per immersion.

Three samples corresponding to the sample of Example 9 are prepared andtheir wet strength measured. The wet tensile strength of the threesamples were 1980 grams, 2016 grams and 2365 grams.

The blue asbestos paper of 0.040 inch thickness and containing 4% buna-Sas a binder material (i.e., the asbestos paper from which theimpregnated samples are made) is cut into three samples of the size andshape required by the wet tensile strength test and soaked in Water atroom temperature for 3 hours before testing. The wet tensile strength ofthese non-impregnated samples is measured and found to be 1270 grams,1420 grams and 1458 grams.

The above tests illustrate the improvement of mechanical strengtheffected by impregnation, in most cases, more than 50% improvement isnoted.

EXAMPLES 12 THROUGH 16 A solution of high melting polyethylene powder(density of 0.90 to 0.92) comprising spherical shaped particles of 30micron minimum size in decahydronaphthalene is prepared. After 30minutes at C. the dissolution is complete and solution is transferred toan immersion tank. A dry crocidolite paper containing 4 weight percentbuna-S rubber binder and having a thickness of 0.020 inch is placedbetween two stainless steel screens and the assembly is immersed forabout 1 to 3 minutes in the imprzeog nting solution in the immersiontank maintained at After immersion the impregnated paper-screen assemblyis withdrawn from the liquid and tilted at a 45 angle over the tank toallow for drainage of mother liquor from the impregnated matrix over aperiod of about 2 minutes. The drained matrix is then transferred fromthe screen as sembly to a vacuum oven where the impregnated matrix isldried at 80 C. for 12 hours on a polished stainless steel p ate.

This procedure of impregnating the blue asbestos paper described aboveis repeated 4 times except that different concentrations of theimpregnant in the impregnation liquid are employed. The permeability ofa non-impregnated blue asbestos paper of the type used in this exampleis compared with the samples impregnated at various concentrations ofimpregnant by the above method and the results of this comparison arereported in Table II.

1 Expressed as head of water pressure in inches at a fixed flow rate 300cc./minute/square foot of diaphragm.

EXAMPLES 17 TO- 22 The same impregnation treatment described above forExamples 13 through 16 is repeated except that a pure crocidolite paperwithout binder or other add tive is employed as the asbestos matrix. Thematrix 1s prepared from a 1% slurry of 35 grams per liter of crocidoliteasbestos fibers in a potassium chloride brine solution at 125 F. and amixing time of 30 minutes. The slurry is transferred to a Hand-sheetpaper making machine where the diaphragm matrix is formed. The water legof the machine is previously filled to the mold level w th a brinesolution (50 grams of potassium chloride per l1ter) and the releasevalve is opened so as to empty the hopper over a period of 2 minutes.

About 120 seconds drain time is allowed for the asbestos matrix on themold after which the asbestos sheet is removed from the mold, placedbetween two polyethylene sheets and pressed in a 40 ton hydrauliclaboratory press at 1000 pounds per square foot. The asbestos sheet isthen dried in an air oven at 110 C. for 20 hours and 5 samples of thispreformed asbestos sheet are subjected to the impregnation treatmentdescribed in Examples 13 through 16. The permeability of the samples isreported in Table III. Example 17 is reported for a sample of this paperwhich is not impregnated.

TABLE III Impregnant solution Wt. percent (grams/ increase Perme-Example liter) of sample ability 1 1 Expressed as head of water pressurein inches at a fixed flow rate of 300 co./miuute/square foot ofdiaphragm.

EXAMPLES 23 THROUGH 26 The same impregnation treatment described forExamples 13 through 16 is repeated except that the asbestos matrixcontains 3 weight to butyl rubber (copolymer of butylene and butadiene)as a binder instead of 4 weight percent buna-S rubber binder. Thepermeability of 4 samples of this matrix (one unimpregnated and 3impregnated) is reported in Table IV.

300 ccJminute/square foot of diaphragm.

EXAMPLES 27 THROUGH 29 The same impregnation treatment described abovefor Examples 13 through 16 is repeated except that the asbestos matrixis 0.040 inch thick and the impregnant is high density polyethylene(density of from 0.94 to 0.96) dissolved in Tetralin. The permeabilityof 3 samples of this matrix (one unimpregnated) is reported in Table V.

TABLE V Impregnant solution Wt. percent (grams/ increase Perme- Exampleliter) of sample ability 1 l Expressed as head of water pressure ininches at a fixed flow rate of 300 cc./minute/square foot of diaphragm.

EXAMPLE 30 The following crocidolite paper diaphragms were measured forwet tensile strength and results reported in Table VI.

TABLE VI Impregnant Wet Paper oi Thickness Binder, CZHi tensile Exampleof sample Permeapercent olymer strength No.- (inch) bility 1 rubberFg/liter) (g U. 04 17. 6 4 buna-S- 20 2, 534

1 Expressed as head of water in inches at a flow rate 01300 cc. perminute per square foot of diaphragm.

EXAMPLE 31 Eight parts of polyurethane resin (density 1.07, viscosity200 poise) is dissolved in 100 parts of methyl ethyl ketone aqueoussolution). About 3 liters of the solution is introduced into animmersion tank wherein it is maintained at C. A dry sheet of amositecontaining 6% buna-S rubber binder having a thickness of 0.030 inch isimmersed in the impregnation solution for 2 minutes and then removed andallowed to drain for 1.5 minutes. The impregnated sample is dried at 60C. for 20 hours in a vacuum oven (15 inch vacuum) after which it issubjected to heat setting at 135 C. and pressed between calender rollersto a thickness of 25 mils. The amount of polyurethane impregnant addedto the asbestos matrix is 2.5% and the permeability measured is 7.0(head of water at 300 cc./minute/square foot of dia- P s EXAMPLE 32 Fiveparts of polysulfide rubber (molecular weight of 4,000) is dissolved in'95 parts of ethyl acetate. About 5 liters of the resulting solution isintroduced into an immersion tank where it is maintained at 85 C. A drysheet of crocidolite paper containing 6% buna-S rubber as a binder andhaving a thickness of 0.025 inch is immersed in the impregnationsolution for 1.8 minutes while agitating. After this period ofimpregnation, the sample is removed from the liquid, drained by passingit at a 45 angle between rollers and dried in a vacuum oven (16 inchvacuum) for 20 hours at 65 C. The amount of copolymer impregnant addedto the asbestos matrix is 3.1 weight percent, and the permeabilitymeasured is 8.3 (head of water in inches at a flow rate of 300 cc. perminute per square foot of diaphragm).

A second solution of 20 parts of polypropylene dissolved in 80 parts ofTetralin is sprayed on the surfaces of the impregnated sample is airdried for 10 hours at a temperature of C. The amount of polypropyleneimpregnant added is 1.5 weight percent and the permeability of thesample is 15.6 (head of water in inches at 300 cc. per minute per squarefoot of diaphragm).

EXAMPLE 33 Twenty parts of polyvinyl chloride resin having an averageparticle size of from about 1 to about 3 microns is added to 80 parts ofisobutanol and dispersed therein. To this dispersion is added 0.2 weightpercent of Methocel as a thickening agent and 0.4 weight percent ofammonium stearate as a surfactant. The mixture is emul- 15 sified in athree-roll paint mill for 15 hours. The resulting emulsion is added toan equal portion of sodium chloride solution in an immersion tank andthe mixture is stirred for one hour at 55 C. Crocidolite papercontaining 3% polypropylene and having a wet tensile strength of 835grams is immersed in the tank for 2 minutes, then drained for 1 minuteand dried at 120 C. for 12 hours. The resulting diaphragm contains 2.5weight percent impregnant and other solids, the permeability is 9.5(head of water in inches at a flow rate of 300 cc. per minute per squarefoot of diaphragm) and the wet tensile strength is 1735 grams.

EXAMPLE 34 Five parts of chloroprene and 5 parts of polyurethane aredissolved in 90 parts of methylene chloride at 70 C. The resultingsolution is sprayed for 15 minutes under a pressure of 25 p.s.i.g. ontoboth surfaces of a crocidolite asbestos mat having a wet tensilestrength of 350 grams. The impregnated mat is dried at 125 C. for 12hours and the resulting diaphragm contains 6 weight percent chloropreneand polyurethane impregnant, the permeability of the sample is 17.0(head of water in inches at 30 cc./minute/square foot of diaphragm) andthe wet tensile strength is 2140 grams.

EXAMPLE 3 5 A liquid permeable diaphragm for use in an electrochemicalsystem for the oxidation of propylene to propylene oxide is prepared byemploying the impregnated blue asbestos paper of Example 1. Thepolyethylene impregnated paper is soaked in hot Decalin (115 C.) for 20seconds, then placed between two polyethylene screens (4 x 4 mesh) andheld in a hydraulic press for minutes at 180 F. under 10 p.s.i.g. Theresulting lamination contains a center layer of impregnated asbestospaper, both sides of which are bonded to a polyethylene screen forreinforcement.

It is to be understood that any of the rubber, thermoplastic, orthermosetting impregnants or mixtures of the impregnants individuallydefined above, particularly the synthetic rubbers and the polymericcompositions of C to C hydrocarbon monomers which are unsubstituted orsubstituted with a halogen, cyano (e.g. CN), amino (e.g. NH acryl (e.g.C H O) or carbonyloxy (e.g. C0.0) group can be substituted in any of theabove examples which are drawn to impregnation to provide an asbestosdiaphragm of greatly improved mechanical strength for use in acontinuous electrochemical process.

It is further to be understood that any of the asbestos matrices, ormatrices containing blends of asbestos or asbestos compositions, such asthose disclosed in copending patent application Ser. No. 814,821, filedApr. 9, 1969, can also be substituted in any of the above examples whichare drawn to impregnation to provide diaphragms of greatly improvedmechanical strength for use in electrochemical processes. Thesediaphragms can be subsequently laminated to a porous metal or plasticsubstrate, if desired.

Having thus described my invention, I claim:

1. A process for producing a diaphragm for an electrolytic cell whichcomprises:

treating a preformed asbestos diaphragm matrix with a preformedpolymeric impregnant in a liquid medium, said polymeric impregnant beingselected from the group consisting essentially of polybutadiene,polyvinyl chloride, polychloroprene, polyisoprene, polyethylene,polybutylene, polypropylene, polyurethane, polychlorotrifluoroethylene,and polytetrafluoroethylene;

heating the resulting wet impregnated matrix in a heating zone to atemperature between about 25 C. and about 400 C., said heating zonecomprising a drying zone wherein the impregnated matrix is dried at atemperature between about 25 C. and about 120 C. and a sintering zonefollowing said drying zone operated at a temperature between about 40 C.and about 400 C. so that at least the impregnated asbestos diaphragm aresoftened; and

laminating said impregnated asbestos diaphragm to a porous metal orplastic substrate at the sintering temperature of the impregnantparticles and under a pressure of from about 10 to about 1500 p.s.i.g.

2. A process for producing a diaphragm for an electrolytic cell whichcomprises:

treating a preformed asbestos diaphragm matrix with a preformedpolymeric impregnant in a liquid medium, said polymeric impregnant beingselected from the group consisting essentially of polybutadiene,polyvinyl chloride, polychloroprene, polyisoprene, polyethylene,polybutylene, polypropylene, polyurethane, polychlorotrifiuoroethylene,and polytetrafluoroethylene;

heating the resulting wet impregnated matrix in a heating zone to atemperature between about C. and about 400 C.;

treating said impregnated matrix with a second liquid medium which is asolvent for the impregnant at a temperature sufficient to soften atleast the impregnant particles on the surface of the impregnated matrix;and

laminating said solvent treated impregnated matrix to a porous metal orplastic substrate by applying a pressure of from about 10 to about 1500p.s.i.g. under a sintering temperature of from about 40 C. to about 400C.

References Cited UNITED STATES PATENTS 3,505,200 4/ 1970 Grotheer204-295 3,501,388 3/1970 Kronig et al. 204-296 3,291,632 12/ 1966Nielsen 204-296 3,276,992 10/1966 Hani 204-296 2,681,320 '6/ 1954Bodamer 204-296 2,967,807 1/ 1961 Osborne et a1. 204-296 2,264,1587/1938 Clark 117-126 AB FOREIGN PATENTS 804,176 11/ 1958 Great Britain204-296 591,327 1/1960 Canada 117-126 AB JOHN H. MACK, Primary ExaminerR. L. ANDREWS, Assistant Examiner US. Cl. X.R.

